Photochemically-removable groups have many applications in bioorganic chemistry. Besides providing deprotection that can be accomplished under conditions that leave most other protecting groups untouched (Pillai, V. N. R, Organic Photochemistry 3:225 Synthesis (1980)), photochemically removable groups can also be used in the technique of caging (Adams et al, J. Am. Chem. Soc. 111:7957 (1989)) wherein a biological molecule is rendered both inactive and membrane-permeable by the protecting group. Once located inside a cell or an enzyme active site (Schlichting et al, Proc. Natl. Acad. Sci. USA 86:7687 (1989)), the protecting group can be released on a time scale much faster than that of the biological or enzymatic process, permitting the study of the time evolution of the phenomena. Photoremovable groups are also key to the novel technique of light-directed synthesis. This technique is used to prepare large arrays consisting of thousands of biopolymer sequences (see Fodor et al, Science 251:767 (1991) and U.S. Pat. No. 5,143,854).
Many of the photoremovable groups currently in use are based on nitrobenzyl photochemistry that produces a byproduct nitrosocarbonyl compound. This substance can create problems with development of intensely absorbing solutions during deprotection and reaction with functional groups such as amines. Nitrobenzylethers can also be difficult to form from alcohols, a functional group commonly requiring protection (Pirrung et al, Bioorg. Med. Chem. Lett. 2:1489 (1992)). The present invention overcomes the problems of prior protecting reagents and provides excellent photochemically removable agents for the protection of functional groups, including primary and secondary alcohols.